Method of manufacturing magnetic drum memory apparatus

ABSTRACT

The memory apparatus incorporates a drum, mounted for rotation, and a series of hard mounted heads, spaced from the drum magnetic recording medium surface. The mounting structure includes spaced parallel aligning bars, utilized to precisely align the magnetic heads prior to finally fixing them to the structure, and resilient plastic wedges utilized to maintain a bias against the aligning bars, to compensate for the stresses induced in the assembly process. The precise spacing from the magnetic medium is accomplished by placing a spacing film over the drum, which film is removed after final assembly, leaving the proper head-tomedium gap. The final configuration is maintained by the use of epoxy adhesive to secure the heads to the aligning bars and retaining bars. The frame structure and head utilize the same metal alloy to maintain the head-to-medium gap during temperature variations. The resulting apparatus may be utilized in a voice response system for producing computer ordered, human voice response, to various commands. In this application the drum is rotated at a rate of one revolution per second and the head gap, head-to-medium spacing, and medium thickness, controlled to produce a relatively flat response characteristics over the frequencies of importance and thereby enable the use of relatively simple amplifiers with linear response characteristics.

United States Patent [191 Roes [ May 28, 1974 METHOD OF MANUFACTURING MAGNETIC DRUM MEMORY APPARATUS [75] inventor: John B. Roes, San Diego, Calif.

[73] Assignee: Metrolab, Inc., a Subsidiary of Cubic Corp., San Diego, Calif.

[22] Filed: Oct. 4, 1971 [21] Appl. N0.: 186,238

[52] US. Cl. 29/603, 179/1002 C, 179/1002 P, 340/174.l E, 340/174.1 F

[51] Int. Cl. Gllb 5/42 [58] Field of Search. 29/603; 340/l74.1 F, 174.1 E; 346/74 MC, 74 MD; 179/1002 C, 100.2 CA,

Van Lammeren et al. 179/1002 P Stark 29/603 X Primary Examiner-Charles W. Lanham Assistant Examiner-Carl E. Hall Attorney, Agent, or FirmBrown and Martin [57] ABSTRACT The memory apparatus incorporates a drum, mounted for rotation, and a series of hard mounted heads, spaced from the drum magnetic recording medium surface. The mounting structure includes spaced parallel aligning bars, utilized to precisely align the magnetic heads prior to finally fixing them to the structure, and resilient plastic wedges utilized to maintain a bias against the aligning bars, to compensate for the stresses induced in the assembly process. The precise spacing from the magnetic medium is accomplished by placing a spacing film over the drum, which film is removed after final assembly, leaving the proper headto-medium gap. The final configuration is maintained by the use of epoxy adhesive to secure the heads to the aligning bars and retaining bars. The frame structure and head utilize the same metal alloy to maintain the head-to-medium gap during temperature variations. The resulting apparatus maybe utilized in a voice response system for producing computer ordered, human voice response, to various commands. In this application the drum is rotated at a rate of one revolution per second and the head gap, head-tomedium spacing, and medium thickness, controlled to produce a relatively flat response characteristics over the frequencies of importance and thereby enable the use of relatively simple amplifiers with linear response characteristics.

4 Claims, 7 Drawing Figures iATENIEflm 28 m4 3:8 1 2.579

sum 1 OF 2 Fig 28 32 34 |0 I4 28 43[ so 53 EN TOR. JOHN ROES BY @W 2 777M ATTOR NEYS minnow 28 m 3.812.579

' SHEEY 2 BF 2 INVENTOR. JOHN B. ROES ATTORNEYS METHOD OF MANUFACTURING MAGNETIC DRUM MEMORY APPARATUS BACKGROUND OF THE INVENTION Numerous applications for voice response systems that can be queried, for example, from a standard desk push button telephone, have been identified. It has been proposed that a magnetic drum memory might be employed to store the necessary recorded words for access from a logic and thereby make up a response in relatively normal speech. However, existing magnetic recording and playback apparatus is not suitable for use in this environment for a number of reasons. Typically, magnetic drum memory apparatus rely upon heads riding on the surface of the magnetic drum, with the attendant problems of wear and reliability. Contacting heads are particularly unsatisfactory in the voice response environment where they would be expected to operate continuously. Conversely, it has not been practical in prior art devices to utilize noncontacting heads with a relatively slowly rotating magnetic drum, because no means of maintaining the proper head-to-drum spacing has been discovered, and this is particularly apparent in devices designed to be operated under ambient conditions, with no control over temperature. Thus with existing magnetic drum recording apparatus, it is not possible to utilize noncontacting heads, because the heads move toward or away from the drum an unacceptable amount, due to manufacturing irregularities or temperature variations and degradate response characteristics or cause the heads to contact with the magnetic drum.

The problems of producing a reliable magnetic drum memory apparatus are particularly apparent when they are considered from a cost standpoint. The cost prob lem is accentuated by the rejection rate associated with existing manufacturing techniques, and the labor required to execute those manufacturing techniques.

Thus there is a need for an improved magnetic drum memory apparatus that is capable of employing noncontacting heads, in a structure that may be assembled with a minimum expenditure of labor, and a minimum exposure to rejection due to improper head-to-medium spacing.

SUMMARY OF THE INVENTION An exemplary embodiment of the magnetic drum memory apparatus of the invention incorporates a rotatable drum, mounted in frame means, which drum has a magnetic recording medium on its outer surface. The frame ends are spaced by parallel aligning bars and retaining bars, at each head position. Each set of aligning bars and retaining bars support between them magnetic recording heads. The heads are maintained in their precisely aligned and spaced position through the use of an epoxy adhesive applied between the heads and one or more of the aligning and retaining bars.

The method of manufacturing the apparatus of the invention includesthe use of a resilient plastic wedge placed between the magnetic heads and the retaining bars to provide a resilient bias of the head against the aligning bars, to compensate for irregularities as a result of bowing of the bars or other manufacturing deviations that would otherwise result in the accumulation of an unacceptably large error. Proper drum-tomedium spacing is obtained by placing of a film, such as a Mylar film, ofa thickness corresponding to the desired head-to-medium spacing over the drum and biasing the heads toward the drum through the use of a spring biased telescoping pin. Thus the head is biased towards the drum and against the aligning bars, and its position is therefore precisely known when the epoxy adhesive is applied. The adhesive, upon hardening, maintains the heads in their final position. After hardening, the assembly jig and Mylar film may be removed.

The security of thefinal head placement will be ensured by the use of a common alloy for the drum and frame so that both the frame and drum grow at the same rate with temperature increase, and the head-todrum spacing varies very little, if at all. The head-to medium spacing is selected as is the medium thickness, to compensate for the normal emphasis on the higher frequencies, and thus to produce a relatively flat response over the voice frequencies range, thereby enabling the use of simple amplifiers with no frequency compensation.

It is therefore an object of the invention to provide a new and improved magnetic drum memory apparatus.

It is another object of the invention to provide a new and improved magnetic drum memory apparatus that is low in cost.

It is another object of the invention to provide a new and improved magnetic drum memory apparatus that is utilizable with relatively simple uncompensated amplifiers.

It is another object of the invention to provide a new and improved magnetic drum memory apparatus utilizing non-contacting heads.

It is another object of the invention to provide a new and improved magnetic drum memory apparatus that maintains head-to-medium spacing despite variations in temperature.

It is another object of the invention to provide a new and improved magnetic drum memory apparatus with provision for aligning and spacing the magnetic heads.

It is another object of the invention to provide a new and improved method of manufacture for magnetic drum memory apparatus.

It is another object of the invention to provide a new and improved method of manufacture for magnetic drum memory apparatus that reduces the number of defective manufactured devices.

It is another object of the invention to provide a new and improved method of manufacture for magnetic drum memory apparatus that reduces the man hours required for assembly.

Other objects and many attendant advantages will become more apparent upon a reading of the following detailed description together with the drawings in which like reference numerals refer to like parts throughout and in which:

FIG. 1 is a top plan view of the complete apparatus of the invention.

FIG. 2 is a side elevation view as taken from below FIG. 1.

FIG. '3 is a sectional view taken on line 33 of FIG.

FIG. 4 is an enlarged view of a portion of FIG. 3. FIG. 5 is a sectional view showing the initial frame and drum assembly.

FIG. 6 is a similar view showing mounting of magnetic heads and a spacing film- FIG. 7 is a similar view showing jig alignment curing of the heads.

Referring now to the drawings, there is illustrated frame means 10, including end frames 12 and 16 and side frame 14. The frame supports a shaft 20 carrying a drum 18. The shaft is mounted for rotataion in bearings 22 in the end frames 12 and 16. The end frames also carry a plurality of aligning and retaining bars. The center lines of aligning bars 32 and 34 lie in a plane which is parallel to a selected radial from the axis of rotation of drum l8 and spaced from that plane by a distance corresponding to one-half of the width of the magnetic head to be employed. Thus when a magnetic head 28 is placed in contact with the aligning bars 32 and 34, its center line axis will correspond to the radial from drum 18. Retaining bars 40 and 42 are utilized to secure the position of the head, after it has been located, by the use of the aligning bars. However the position of bars 40 and 42 is not critical since the actual alignment takes place with respect to bars 32 and 34 and for this reason retaining bars 40 and 42 are spaced from the center line of the head an incremental distance sufficient to allow for the placement, between the head and retaining bars, of a resilient plastic wedge 43.

trated at numerals 36 and 38 and cooperate with retaining bars 44 and 46. A plurality of recording heads 26 are supported between these bars, and secured thereto, by the application of an epoxy adhesive 56 at numerous points between the aligned bars and retaining bars. For purposes of clarity, the adhesive has been omitted from FIGS. 1 and 2. The two spaced banks of bars are interconnected through a rigidizing block 48 to complete the structural interconnection.

Referring now to the detail of FIG. 4, the head 28 is shown to comprise a body portion 29 and electrical connectors 50 and 52. An additional pair of electrical connectors 53 and 55 is best seen in FIG. 2. Also illustrated in FIG. 4 is the placement of resilient plastic wedge 43 between the retaining bars 40 and 42 and the head body 29. The plastic wedge may comprise, for example, a nylon thread, 40 mills in diameter. The gap portion of the head 54 is illustrated as being spaced from the magnetic medium surface 24 of the drum 18. This spacing is produced in a manner to be described more fully hereinafter.

The output characteristics of the heads are varied by varying the head to-medium spacing, as well as the depth to which the drum surface is magnitized. These two variables may be employed to produce a substantially linear output of the head with respect to frequency variation and therefore no compensation need be provided for in the amplification of the heads output, substantially reducing the complexity of the electronics required. It is possible to hold a flat frequency response t3 db over the range from 300 to 4,500 htz.

The method of making the apparatus of the invention is illustrated in FIGS. to 7. An initial assembly illustrated in FIG. 5 is made up, comprising the frame strucand seture l0'and the rotatably mounted drum 18 together with a plurality of aligning and retaining bars.

The aligning bars 32 and 34 and 36 and 38 are precisely positioned and secured to the frame in a suitable manner. The use of cylindrical aligning bars has particular advantages when used with the invention, due to the fact that a cylindrical bar is not sensitive to the rotational position of the bar, whereas a flat unitary or double aligning bar, would have a rotational positioning requirement. The retaining bars are secured in position but need not be precisely located, since the plastic wedge provides for some tolerance. In the second phase of assembly illustrated in FIG. 6, a Mylar film 58 is placed over the drum 18, to act as a spacer, so the recording heads 28 may be placed in position between the aligning bars and retaining bars against the Mylar film. A plastic wedge 43 is placed between the head and retaining bars for each head to be affixed to the apparatus and therefore the load delivered by the retaining bars to the aligning bars can be predetermined to a more precise extent.

FIG. 7 illustrates the resilient load that is applied to the heads, to bias the heads toward the drum. For this resilient biasing purpose, a fixture of jig 62 is utilized, which jig has a spring biased telescoping pin 66 having a tip 68 that contacts the rearward surface of each magnetic recording head to be affixed to the structure. A spring 70 is utilized to apply a bias to the head and bears against shoulder 72 on the pin and against surface 74 on guide block 64. The guide block is secured to the jig frame 60..Also illustrated in FIG. 7 is the epoxy 56 being applied through an applicator tip 61. The epoxy would be applied to all of the joints between the aligned bars and head, and the retaining bars and head, and then would be allowed to set. i

After the adhesive has hardened so that the structural interrelationship between the head and drum is fixed, the jig 62 may be removed from the structure, and the film 58 withdrawn from the gap between the head and drum, whereupon the apparatus of the invention is ready to be connected to the appropriate electronic circuitry and utilized in the manner to be described hereinafter.

OPERATION The apparatus of the invention has particular applicability to use with voice response systems, where its high reliability and long operating life are particularly useful. For use with these systems a drum speed of approximately 1 revolution per second would be selected, whereby a word repeated on a track once, would be acce sible at a maxim m Eatery?! tg ia-bai i nc. 2?- ond. That is, each track of the 20tracks illustrated for the exemplary embodiment, would have access to one word or phrase magnetically recorded in the medium on the drum surface. Thus if logic circuitry determined that the word or phrase recorded on a particular track was to be accessed, the output of thathead would be monitored until a strobe pulse was detected, then that channel would be placed on line, and the word or phrase of approximately one-half second duration read by, and utilized by, the circuitry to produce a readout of the word, which when amplified by appropriate amplifiers would be delivered to the user in the form of a yoice response. .In the instant embodiment, the logic has access to 20 channels and can put together simple sentences, or other phrase responses, depending on the vocabulary originally recorded into the drum surface. biasing said magnetic heads radially into contact with For example, channel 1 might include the phrase the said film and holding said magnetic heads against reading is and this phrase could be utilized in conjuncid fil tion with numerals recorded on channels 2 through ecuring aid head in position and and the work point recorded on channel 11 to pro- 5 removing Said fl| duce a voice response as follows. the reading is one The method of claim 1 whergin Said alignment two five point four. means is characterized by:

Havmg descr'bed my mvemlon I now claim: at least two radially spaced cylindrical alignment 1. A method of mounting a plurality of magnetic heads from supporting structure in radial alignment and spaced from the surface of a rotatable magnetic memory drum, comprising the steps of:

placing a film sheet over said memory drum,

inserting each magnetic head and a resilient wedge between spaced parallel aligning and retaining means with a first side of said magnetic head contacting and being positioned by said aligning means bars.

3. The method of claim 1 wherein:

said step of biasing said magnetic head is characterised:

applying radial spring pressure.

4. The method of claim 1 wherein said step of securing said heads in position comprises:

applying adhesive between said magnetic heads and and the opposite side of said head being held in a said supporting struct spaced relationship from said retaining means by and allowing said adhesive to set. said resilient wedge, 

1. A method of mounting a plurality of magnetic heads from supporting structure in radial alignment and spaced from the surface of a rotatable magnetic memory drum, comprising the steps of: placing a film sheet over said memory drum, inserting each magnetic head and a resilient wedge between spaced parallel aligning and retaining means with a first side of said magnetic head contacting and being positioned by said aligning means and the opposite side Of said head being held in a spaced relationship from said retaining means by said resilient wedge, biasing said magnetic heads radially into contact with said film and holding said magnetic heads against said film, securing said head in position, and removing said film.
 2. The method of claim 1 wherein said alignment means is characterized by: at least two radially spaced cylindrical alignment bars.
 3. The method of claim 1 wherein: said step of biasing said magnetic head is characterised: applying radial spring pressure.
 4. The method of claim 1 wherein said step of securing said heads in position comprises: applying adhesive between said magnetic heads and said supporting structure, and allowing said adhesive to set. 